Allow larger strings for descriptions

[b-per]

This is a:

• bug fix PR with no breaking changes
• new functionality

Link to Issue

Fixes #437

Description & motivation

This change allows Redhsift users to define a larger varchar size for the description column, without having to change the default size for every varchar column.

Integration Test Screenshot

Checklist

• I have verified that these changes work locally on the following warehouses (Note: it's okay if you do not have access to all warehouses, this helps us understand what has been covered)
  • BigQuery
  • Postgres
  • Redshift
  • Snowflake
  • Databricks
  • DuckDB
  • Trino/Starburst
• I have updated the README.md (if applicable)
• I have added tests & descriptions to my models (and macros if applicable)